On the contrary, dietary iron, the kind you need, is just iron. There's a fairly common science demonstration where you blend up fortified breakfast cereal (I saw it done with corn flakes) and pass a magnet over it. The magnet will pick up a bit of iron dust.
The amount of steel flaking off a knife into any given meal is likely much smaller than how much iron is in the food on its own merits.
There's also using cast iron to introduce iron into the diet.
Food prepared in iron cooking pots as an intervention for reducing iron deficiency anaemia in developing countries: a systematic review - https://pubmed.ncbi.nlm.nih.gov/12859709/
My search-fu is failing me at the moment, but that was also believed that this was an important part of the pioneers heading west in the early parts of United States history.
The amount of steel flaking off a knife into any given meal is likely much smaller than how much iron is in the food on its own merits.